One feature of vapor phase and bulk phase commercial polymerization techniques for preparing polyolefins with anionic catalysts is that catalyst residues and low-molecular-weight and amorphous polymers are not separated as completely (or at all) from the polymeric products prior to polymer use. Polymeric products made using a liquid preparative medium, e.g., in a slurry or solution process, are generally washed during and after the polymerization process which removes such impurities before the polymeric product is fabricated into shaped articles. The presence of catalyst residues and low-molecular-weight and amorphous products in the polymeric product creates problems in the further treatment of such polymers, e.g., molding, film making, fiber preparation, etc. Such problems include, inter alia, die smoking during film extrusion, thermal degradation during extrusion or shaping operations, yellowing, decreases in brightness, and decreased clarity in polymer films. Thus, in addition to stabiizers usually added to polyolefins made by slurry or solution polymerization techniques, other stabilizers capable of forming complexes with ionic catalyst residues and negating the effects of unseparated materials are required.
Now it has been found that by utilizing compounds which are the partial esters of low to moderate molecular weight polyhydroxy compounds containing two (2) or more hydroxy groups with long chain monocarboxylic acids wherein, preferably, one hydroxyl group has been esterified, or combinations thereof with certain organophosphite, organothiophosphite or organothioglycolylphosphite esters as stabilizers, ionic catalyst residues contained in normally solid, crystalline, high-molecular-weight polyolefins prepared by essentially solventless polymerization processes are tied up such that the deletarious effects of the catalyst residues and other incompletely removed materials, such as low molecular weight and amorphous components, are largely or completely solved.
Prior art which may be considered relevant to the present invention includes Japanese Pat. No. 4271 which is directed to the use of esters of pentaerythritol and combinations thereof with esters of glycerin as antifogging agents in polyolefins. According to the patentees, combining such materials with polyolefins result in a distribution of hydrophilic groups throughout films and other articles prepared from the polymeric compositions and these hydrophilic groups aid in distribution of water over the surfaces of the articles thereby preventing agglomeration of the water and formation of droplets. This reference does not suggest that the disclosed esters improve the stability of polyolefins during fabrication of useful articles therefrom or that the articles exhibit improved resistance to discoloration upon aging. Further, there is no suggestion that the disclosed esters from complexes with ionic catalyst residues contained in polyolefins prepared by essentially solventless polymerization processes so as to substantially prevent the catalyst residues from contributing to processing and other difficulties.
U.S. Pat. No. 3,773,716 is directed to the use of a variety of organic compounds containing P-S bonds, including trithioglycolyl phosphites, as flame retardants, antioxidants, and thermal and U.V. stabilizers for various polymers including polyolefins. It is disclosed that such compounds can be combined with additional stabilizers including organosulfur compounds such as pentaerythritol tetra(mercaptoacetate); phenolic antioxidants; epoxy compounds such as glycidyl ethers of glycerine, pentaerythritol, and sorbitol; and phosphite and thiophosphite stabilizers such as tristearyl phosphite, trilauryl phosphite, trilauryltrithiophosphite, tri(nonylphenol)phosphite, and tris-(4-methylthiophenyl) phosphite. The patentees also disclose that catalyst residues and other impurities adversely affect the thermal stability of polypropylene and other monoolefin polymers, and that polyvalent metal salts of fatty acids can be added to such polymers to impart thermal stability thereto.